1. Field of the Invention
The present invention relates to a plastic screw-type bottle cap comprising a cap body with an internal thread and a tamperproof strip. The latter has flanges disposed on the inside thereof, is non-breakable and is connected by webs to the cap body. As the cap body is unthreaded from the bottle the tension or strain in the webs increases causing the latter to break. The tamperproof strip includes an expansion means with at least one permanent connection disposed in the area between the tamperproof strip and the cap body.
2. Description of the Prior Art
Screw-type caps of this type are widespread and are used in particular on glass or plastic beverage containers. Such bottles are produced in a variety of standard sizes and are circulated in large numbers, either in returnable or non-returnable form. In particular it is the standardized bottle neck and accompanying thread in bottles of this type that make it possible, despite differences in bottle sizes, to employ a uniform screw-cap. Though this offers many advantages, there is one distinct disadvantage, in that with the continously large number of bottles in circulation, it is virtually impossible to alter the geometry of the bottle neck. As a result, screw-caps, as so-called disposable articles, must be adapted to the geometry of a given bottle neck or thread configuration. Within the bottle-neck-screw-cap system, therefore, modifications are economically feasible only with regard to the screw-cap.
Known screw-type plastic bottle caps are generally comprised of a cap body with an internal thread and a tamperproof strip. Conventionally, the tamperproof strip is made so that it detaches at least partially from the cap body when the cap is unthreaded. This is intended as an indication to the consumer that the bottle was either previously opened, or has not yet been tampered with.
Normally, the tamperproof strip is in the form of a ring connected to the cap body by thin webs. In addition, flange-like elements or lamellae are provided on the inside of the tamperproof strip which form a so-called stop ring when the cap is screwed on, and which engage the stop ring on the bottle from behind. Such a stop ring is usually formed on the neck of the bottle immediately below the external thread near the body of the bottle and, in standardized form, has an equivalent or slightly larger diameter than the external thread disposed immediately above it. Due to the slightly conic inclination of the stop ring where it meets the body of the bottle, the tamperproof strip expands circumferentially outward somewhat as a result of inherent elasticity of the plastic material used. The flanges or lamellae formed on the inside of the strip are thus able to slip past the stop ring and lock in place once the cap is completely threaded on, thereby engaging the stop ring from behind.
As the bottle is sealed, the flanges or lamellae secure the tamperproof strip to the stop ring, while webs, designed as predetermined breaking points, break as a result of the tension placed on the plastic material. The fractured connection between the tamperproof strip and the cap body is a direct indication that the bottle was previously opened.
Tamperproof strips are known in basically two different embodiments. In the first tamperproof strip embodiment, the strip detaches completely from the cap body as the latter is unthreaded, and it remains behind as a ring on the neck of the bottle. This embodiment is disadvantageous, however, particularly with regard to waste disposal. Because the tamperproof strip remains on non-returnable bottles, which are melted down after one use, the resultant melt becomes contaminated. In the case of returnable bottles on the other hand, the old tamperproof strip must be removed prior to refilling and resealing before the new screw-cap can be attached.
Environmental factors as well do not favor this embodiment, since it is entirely possible that the tamperproof strip stuck initially to the neck of the bottle may become detached and lost in the environment as undesirable litter.
Esthetic considerations, an ever stronger selling point, are a further reason against the tamperproof strip remaining on the neck of the bottle, as this is considered a nuisance by many consumers.
The second known tamperproof strip embodiment ruptures when the screw-cap is removed, but otherwise remains attached to the cap body. Here, the protruding ends of the tamperproof strip are considered especially disadvantageous because they are a nuisance to the consumer while threading and unthreading the cap, and they may result in bodily injury. Esthetic considerations also weigh against the use of this tamperproof strip embodiment, as the protruding ends are found to be a nuisance by the consumer.
The closest cited prior art is U.S. Pat. No. 5,246,125. The screw-type cap disclosed therein possesses the features set forth above. When threading and unthreading this screw-cap from the bottle, the tamperproof strip expands in an axial direction due to an expansion means and is held in place at a connection point located near said expansion means. This action presents serious problems, however, when the mold is released during the manufacturing process, because even as the mold is released a tension is placed on the webs between the tamperproof strip and the cap body, and thus they tend to break during manufacturing.
Another screw-type plastic cap is known from German patent publication DE-A-42 6 123, in which a tamperproof strip is also connected by webs to the cap body. The tamperproof strip of this screw-cap also has an expansion means, but it too only expands in an axial direction.